The invention relates to a system for the removal of material from the surface of a sample by the use of a high-frequency plasma produced in front of the sample surface.
From Applied Physics, vol. 14 (1977), pp. 43 to 47, it is known to sputter particles from the surface of a plane sample with the aid of a plasma and to subject these particles to chemical analysis by the use of a mass spectrometer. The plasma serves both for the formation of the ions producing the sputtering and for the post-ionization of the removed neutral particles which are analyzed with the mass spectrometer. Unlike the SIMS (Secondary Ion Mass Spectrometry) method, this known SNMS (Sputtered Neutral Mass Spectrometry) method permits quantitative determination of the chemical composition of the sputtered particles, and hence of the sample.
From the publication cited, there is further known a method of removing material from the surface of a sample in the form of atomic layers so as to permit depth-profile analysis. To obtain accurate results, the lateral removal of the material must proceed with extreme consistency, regardless of whether the particles or layers removed are analyzed by the SNMS or another surface-analysis method.
Uniform removal of areas of layers is desirable in many cases, as in the investigation of diffusion or implantation profiles, of transition regions in thin multilayer systems, and in other boundary-layer problems. Even in ionic etching which is not followed by analysis of the removed particles it is usually desirable that the material be removed as evenly as possible.